"Rack is generally used for a body of clouds, or rather for the course of clouds in motion."
I add a few instances of the use of this word, many of which are collected in the note I have referred to.
In Antony and Cleopatra—
"That which is now a horse, even with a thought
The rack dislimns."
In Fletcher's Faithful Shepherdess—
"shall I stray
In the middle air, and stay
The sailing rack."
In Dryden's tenth Æneid—